1. Field of the Invention
The present invention relates to an optical waveguide for a touch panel.
2. Description of the Related Art
Touch panels are input devices for operating an apparatus by directly touching a display screen of a liquid crystal display device or the like by a finger, a special stylus or the like, and include a display which displays operation items, and detection means which detects the position (coordinates) of a portion of the display screen of the display touched by the finger or the like. Information of the touch position detected by the detection means is sent in the form of a signal to the apparatus, which in turn performs an operation specified by the touch position. Examples of the apparatus employing such a touch panel include ATMs in banking facilities, ticket venders in stations and portable game machines.
A detection device employing an optical waveguide is proposed as the detection means for detecting the finger touch position on the touch panel (see, for example, US 2006/0002655A1). The touch panel includes a rectangular frame lens provided on the periphery of the display screen of the rectangular display. A rectangular tubular lens fixture frame integrated coaxially with the frame lens is fitted around the periphery of the display, whereby the frame lens is fixed to the display. The optical waveguide is wrapped around the periphery of the lens fixture frame. The optical waveguide includes a multiplicity of cores through which light passes. With the optical waveguide in the wrapped state, one end face (a light outlet or inlet) of each of the cores is directed toward the frame lens. In each of two pairs of opposed portions of the optical waveguide, light beams emitted from cores in one of the opposed optical waveguide portions are deflected by a portion of the frame lens to travel parallel to the display screen of the display toward an opposed frame lens portion, and further deflected to be incident on cores in the other of the opposed optical waveguide portions by the opposed frame lens portion. The optical waveguide and the frame lens thus arranged cause the light beams to travel in a lattice form on the display screen of the display. When a portion of the display screen of the display is touched by a finger in this state, the finger blocks some of the light beams. Therefore, the position of the portion touched by the finger is detected by detecting a light blocked portion on a light receiving side of the optical waveguide.
However, the optical waveguide of Patent Document 1 is bent to have a smaller curvature radius at corners of the periphery of the rectangular display. Therefore, the optical waveguide is liable to be broken due to a load, and suffer from an increased optical loss.
In view of the foregoing, it is an object of the present invention to provide an optical waveguide for a touch panel which ensures prevention of the breakage of its bending portions and reduction in light loss.